FIG. 18 is a view illustrating a configuration of a receiving unit 20 of a power line communication system in later-described Patent Document 1. The receiving unit 20 is constituted by a current detecting unit 21, an average value detecting unit 22, a comparison unit 23, a PN code generation unit 24, a spread spectrum demodulation unit 25, a difference value detecting unit 26, a weighting calculation unit 27, an integration unit 28 and a data judgment unit 29. The average value detecting unit 22 and the comparison unit 23 constitute a demodulation circuit 30.
The current detecting unit 21 detects and outputs a value of a current flowing in a current line L, namely, a current value of the current line L. The average value detecting unit 22 asks and outputs an average value of the current values flowing in the current lines L. The comparison unit 23 has a function comparing a size of the current value according to a current value signal detected by the current detecting unit 21 relative to average value information outputted from the average value detecting unit 22, and outputting the result of the comparison as an ASK (Amplitude Shift Keying) demodulation signal, namely an ASK demodulation function. The PN code generation unit 24 generates and outputs a spread signal based on a predetermined spread code. The spread spectrum demodulation unit 25 inversely spreads the ASK demodulation signal outputted from the comparison unit 23 by using the spread signal of the PN code generation unit 24. The difference value detecting unit 26 asks and outputs a difference value of the current value signal outputted from the current detecting unit 21 relative to the average value information outputted from the average value detecting unit 22. The weighting calculation unit 27 performs a weighting for the inverse spread demodulation signal inversely spread and demodulated by the spread spectrum demodulation unit 25 based on difference value information outputted from the difference value detecting unit 26. The integration unit 28 integrates and outputs the inverse spread demodulation signal after weighting weighted by the weighting calculation unit 27 with a predetermined cycle unit. The data judgment unit 29 performs a binary judgment of integrated value information from the integration unit 28 based on a predetermined threshold value, and outputs a received data (received information signal).
Besides, a circuit to demodulate a voltage which is ASK modulated by changing an amplitude between low-level and high-level is described in later-described Patent Document 2.
Patent Document 1: Japanese Patent Application Laid-open No. 2005-142778
Patent Document 2: Japanese Patent Application Laid-open No. 2006-502684